Adhesively bonded hardware, which are fasteners such as nutplates, bushings, threaded inserts, sleeves, mounts, brackets, etc., are commonly used to secure structural elements during installation or repair. Bonded hardware is used on variety of systems including: aircraft, spacecraft, watercraft, automobiles, and industrial equipment. Adhesively bonded hardware is also used to join components of dissimilar materials or when welding or riveting is not an option. Bonded hardware typically experiences failure in the form of mechanical wear, structural deformation, or separation of the hardware from the mounting substrate (i.e., disbond).
Damaged hardware found during routine maintenance requires timely replacement and approved repair techniques often mandate the use of certified adhesives. Unfortunately, approved repair adhesives are typically those used during original factory installation. Approved hardware adhesives are generally two-part epoxies whose performance specifications are determined by a lengthy cure (e.g. 24 hour) at room temperature. This specific curing time is necessary for the adhesive to develop the strength required to hold the hardware in place for attaching other components (e.g., reattaching an access panel to an aircraft). This long cure time can negatively impact the system's availability.
To expedite bonded hardware installation and repair processes, supplemental heating has been considered in order to accelerate the curing rate of adhesives. However, the accelerated cure profile must be well controlled to achieve desired adhesive properties (e.g., tensile strength, shear strength, peel strength, etc.) and hardware load ratings (e.g., push-out force and maximum torque) while also preventing damage to the surrounding structure due to excessive temperature exposure. Moreover a potential safety hazard is present when delivering heat to bonding locations in an environment where flammable liquids or vapors are present (e.g. aircraft fuel bay).
Specifically, in the aerospace industry, nutplates are commonly attached to aircraft panels. In this case, the 24 hour curing time is highly problematic, because this long cure time can negatively impact the aircraft's availability. To expedite nutplate repair processes, supplemental heating has been considered in order to accelerate the curing rate of adhesives. However, the accelerated cure profile must be well controlled to achieve desired adhesive properties (e.g., tensile strength, shear strength, peel strength, etc.) and nutplate load ratings (e.g., push-out force and maximum torque) while also preventing damage to the surrounding structure due to excessive temperature exposure. Moreover, the delivery of heat to the bonded nutplate area poses issues, because delivering heat in an aircraft environment with flammable liquids or vapors present is a potential safety hazard.
Accordingly, there is a need for improved bonded hardware cure systems capable of reliably and safely reducing the adhesive cure time.